The Large Hadron Collider is the largest and most powerful machine ever built—a 16.5-mile circular tunnel under the French-Swiss countryside, lined with superconducting magnets and designed to accelerate protons to 99.9999991 percent of the speed of light and then crash them into each other. Here the author of such popular science classics as Fermat's Last Theorem, God's Equation, and Descartes' Secret Notebook takes us on a tour of this singular facility, whose purpose is to re-create the immensely hot and dense conditions that existed within the first trillionth of a second after the Big Bang, and introduces us to the scientists who hope it will confirm key theories in physics and cosmology.